Electrical control system



'Jdl/RCE OF March 20, 1945.

E. S. BRISTOL ELECTRICAL CONTROL SYSTEM Filed Aug. 27,

CURRENT JOURCE OF CURRENT AIM/T 5W/7CHE6 INVENTOR. fzdu/arddBmsil (0M.Qzfu/ ATTORNEY.

Patented Mar. 20, 1945' 2,371,732 ELECTRICAL con'mor. sYs'rEM Edward S.Bristol, Philadelphia, Pa, assignor to Leeds and Northrup Company,Philadelphia, Pin, a corporation of Pennsylvania Application August 27,1942, Serial No. 456,428

6 Claims.

of said condition.

In accordance with my invention, aforesaid responsive member, suchas-the pointer of a Bourdon tube, galvanometer or the like, normallytree to respond to changes in magnitude of the controlled condition, isintermittently-engaged by a slidewire, or equivalent impedance, of abalanceable network to include in the network a relay, or equivalent,which upon unbalance of the network effects rebalancing adjustment of asecond impedance concurrently with adjustment of a valve, rheostat orother control member; more particularly, the responsive member, if awayfrom its neutral position, corresponding with a selected fixed magnitudeof such condition, when engaged by the slidewire, is displaced therebyto efiect operation of areversing switch controlling relatively slowadjustment of other impedances in the balanceable network to precludestable balance thereof except with said responsive member at neutralposition. s

My invention further resides in systems and apparatus having thefeatures hereinafter described and claimed.

For an understanding of my invention, reference is made to theaccompanying drawing in which: v

Fig. 1, in perspective, shows significant elements of the controlapparatus;

Fig. 2, shows elements of Fig. 1 in side elevanitude of. acondition tobe controlled, so that its position substantially continuouslcorresponds movement, of frame 5 about its pivots 6 toward and from theposition shown in Fig. 2. Frame 5 carries form 1 upon which is wound theslldewire 3 of a Wheatstone bridge N, Fig. 4, including a secondslidewire l6 and end resistances 160. One of the conjugate arms of thebridge includes the relay to, or equivalent device, responsive tounbalance of the bridge and capable of distinguishing between the twopossible senses of unbalance.

Once for each revolution of shaft 3, the frame 5 is permitted by cam 4to be moved by its biasingspring 9 to effect engagement of contact orpointer l with the slidewire 8 and so complete that arm of the bridgenetwork which includes the differential relay to, or equivalent. For asubstantial fraction of each revolution of shaft 3,

the pointer is free to respond to any change in the condition undermeasurement, for example, pressure, without restraint by engagement withslidewire 8.

If-.,when pointer I is engaged by slidewire 8, the

network N is in balance there is no deflection of The armature of'motorI 4 is suitably mechan-- ically coupled to cheat relative adjustment ofslidewire l6 and contact I! in engagement therewith and the motorwindings or connections are so poled that the adjustment of slidewire I6for either sense of deflection of relay contact H is in proper sense toeffect rebalance of network N. The rotor of motor I! may be alsosuitably mechanically connected to the valve l8, genericallyillustrative of a control member whose position ailfects the magnitudeof a condition to which -pointer l is responsive. For example in acombuswith the existing magnitude of the condition whlch for brevity infurther explanation, may be assumed tobe the pressure of steam in aheader or supply line.

. Upon the shaft 3, r0 at suitable rate, ,for example fifteenrevolutions per minute, by a mo- -tion control system, the member I8 maycontrol e rate of supply of air or fuel to the furnace of a steamgenerator; as exemplary of systemsin which the rate of supply of air orfuel is determined by the setting of a rheostat or valve, reference ismade to my Letters Patent Nos. 1,851,- 974; 1,854,922; 1,870,984. v v

For large sudden changes in position of pointer I, the portion of theimmediately subsequent cycle for which motor I4 is energized may be tooshort to afford sumcient time for complete restor, is mounted cm 4 whichcontrols rocking s5 tornticn of, balance of the network and severalcycles may elapse before that result is attained. However, the power andspeed or motor M should be suiiiciently great to insureclosecorrespondence of the positions of contact I and I! with .respectto their associated slidewires even for rapid changes of the controlledcondition. a

As thus far described, for each different magnitude of the controlledcondition with the'control range, there is a corresponding position ofpointer 'i and of contact ii, and in dependence upon the load, thenetwork N eventually comes to balance with pointer I displaced from theposition corresponding with the mean magnitude of the controlledpressure or other condition. This may be objectionable in systemssubiect to wide variations in load.

To'prevent the network N from remaining in balance for any position ofcontact I except that position thereof corresponding with the meanpressure or temperature, thereare provided the two switch operatingmembers I9H, I9L, the arms 20, 2!] ofwhich are spaced from each other bya distanceslightly exceeding the width of the pointer I so that when thepointer is in its neutral position corresponding with the mean temtweenthe ends of arms 20, when deflected by engagement with the slidewire 8.

If however, when bent back out of its normal plane of movement by theslidewire 8, the pointer I is displaced fromits neutral position itengages one or the other of the members I9H, ISL depending whether thepressure or temperature is above or below normal, and causes it toswing.

movement of one or the other of contacts 22, 23 of reversing switch 24.The fixed pivots 2| is so shaped that the portion of the cycle for whichthe reversing switch is closed is at least roughly proportional to theestent of displacement of pointer I from its neutral position.

The closure of reversing switch 24 effects rotation in one direction orthe other of reversible motor 25 whose armature is mechanically coupledthrough suitable reduction gearing to the moveable elements of thedroop-correction slidewires 26, 21 oppositely adjusted in unison bymotor 25 in sense tending slowly to unbalance network N effectively inopposition to the relatively rapid In consequence upon occurrence of asudden change in position of pointer I with respect to slidewire '8,there is substantially immediately efiected in the next cycle or so ofthe control apparatus, a large. adjustment of valve I8 and of slidewireI6 in sense proper to rebalance network N at the new position of pointerI;'in all subsequent cycles, until the control action causes 'slidewires26 and 21v are slowly adjusted by motor 25 in sense simulating furtherslight changes in the same direction as the original departure fromnormal of the controlled condition. Con-- ment of valve I8, orequivalent control member, it is subjected to additional smalleradjustments sure or temperature is returned to its original desiredmagnitude. will however in general be different than before independence upon factors of 7 operation of the system including the loadupon it.

To utilize the apparatus of Fig. 1 as a master perature or pressure itmay enterthe gap bas of members I9H, ISL are so located and cam 4 7 thelike, for controlling for example the supply of air and iuel to afurnace, or air and/or fuel to di'fierent furnaces there isprovided, asshown or suggested in Fig. 4, for each of the additional controlmembers, its individual controlling motor (MA) coupled thereto and tothe corresponding slidewire (86A). Motor A, for example, is controlledby relay WA, or equivalent, individual to a network NA which, for thefull line position of switch 33 and closed position of switch X,includes slidewire 88A, individual to network NA and also the slidewires26, 21 and com= mon to all of the networks; similarly, each oi theadditional networks NB-NN includes the slidewire 8 in two of its arms.The networks N-NN and the motors may be energized from one or moresources of current, alternating or direct, or as shown, from a singlesource of alternating current I5.

All of the networks N-NN are unbalanced once respond to the mastercontroller in maintenan'ce of a, desired header pressure by control oithe rate of supplymf fuel and/or air to the rebalancing adjustment ofslidewire I6 by motor I4.

individual furnaces of the generators. v

With each of valves I8--I8N, or equivalent. is associated a. pair oflimit switches (HIB, LI.) to interrupt a circuit of motor 25 when thevalve has been moved to ,either limit of its range .of adjustment. Forexample if the open limit switches are in parallel when all of limitabout its pivot 2| and S0 eflect circuit closing 85 .switches 8 |3 areopened because of rival of all of valves I8I8N to fully open position,motor 25 cannot be energized to eflect adjustment of resistances 26, 21in that sense requiring further opening of thevalves; however becauselimit switches LI 8LI8N are closed, motor 25 can be energized foradjustment of resistances 26, 2'lin the opposite direction. Similarlywhen all oi valves I8-l8N have been moved to minimum open, or fullyclosed, position, the corresponding "close limit switches (LI8-LI8N) areopened to prevent energization of motor 25 in that sense for whichresistances 26, 21 are adjusted to simulate further rise in pressure;motor 25 can however be energized in reverse direction when the-pressurehas fallen '-LI8'LI8N are in series with each other, instead p'ointer Ito return to its neutral position, the so sequently after the firstlarge corrective adjustes in one sense or the other until finally thepres-r The position of the valve suited for intervention of manualcontrol because i of in parallel, arrival of the movable element of anyof valves I8I8N to minimum open, or fully closed, position preventsfurther energize.- t'ion of motor 25 in sense,-but only in that sense,simulating further rise in pressure.

By throwing switch 33 from full-line to dotted 5 line position, each ofrelays IDA-I 0N responds to any difl erencebetween the positlonof itsassociated controlled member I8A-I8Nand the posi- :tion of thecontrolled member I8. With this modification, the members I6A-' I8N arenot directly controlled by pointer I but by slidewire I6. Among otheradvantages, this modification is well manual resetting of the mastercontrol member 'I 6 controller for two or more valves, rheostats, or iall hat is nec a y to eff adjustmnt 0f all of the controlled membersl8A-IBN to their corresponding positions.

In that form of the control apparatus shown in Fig. 2, the pointer litself serves as the slidewire contact but it is desirable to avoidpassage of current through the bearings of a relatively delicateinstrument. Therefore, as shown in Fig. 3, the pointer I may be ofinsulation carrying at its end a light contact member IA which serves tocomplete the galvanometer arm of bridge N when engaged by slidewire 8and forced by it into engagement with one or the other of a pair ofcontact bars 28A each connected to lead 28. The contact bars 28A aresupported respectively by pivoted members 29L, 29H (only one of which isshown), which may also correspond in function with the members I9L, NEof Fig. 1, when it is desired to incorporate droopcorrection. Preferablythe members 29L, 29H

are each biased as by a spring 30 into en- 1 gagement with a stop 3|which positions the bars "A very close to but out of contact with thepointer l. The-extent to which the pointer I may be bent by slidewire 8may if desired be limited by stop 32 or by the shape of cam 4.

The contacting surfaces of slidewire 8 (Figs. 2, 3), contact I (or IA)and contact bar 23A (Fig. 3) are maintained clean by their wiping orrolling engagement in each cycle of the control apparatus so ensuringreliable operation even though the apparatus is exposed to dustyatmospheres.

What I claim is:

1. A control system including a balanceable network comprisingimpedances, electro-responsive means. a movable member positioned inaccordance with the magnitude of a condition. reversing members disposedon opposite sides of the desired neutral position of said movablemember, means intermittently to effect engagement 4 of said movablemember with one of said impedances to eflect response of said responsive'means to unbalance of said network and, when displaced from neutralposition, to effect actuation of, one or the other of said reversingmembers, means controlled by said responsive means to eflect rapidrebalancing adjustment of said network, and means controlled by saidreversing members to eflect a slower, unbalancing adjustment of saidnetwork.

2. A control system including a balanceable network comprisingimpedances, electro-respon- 'sive' means, a movable member positioned inaccordance-with the magnitude of a condition,

reversing members disposed on opposite sides of the desired neutralposition of said movable member, means intermittently to effectengagement of said movable member with one of said impedances to effectresponse of said responsive means to unbalance of said network and, whendisplaced fromneutral position,to effect actuation of one or the otherof said reversing members, a controlled member having a range ofadjustment, means controlled by said responsive means for effectingrapid ,rebalancing adjustment. of said network and concurrent adjustmentof said controlled'member, and means controlled by said reversingmembersto eflect slow'unbalancing adjustment ofsaid network whichcontinues so long as said movable member is displaced from its aforesaidneutral positionand the position of said controlled member isintermediate the limits 0f aforesaid range.

3. A system for regulating the magnitude of a condition comprising abalanceable network, electro-responsive means, a movable memberpositioned in accordance with the magnitude of said condition, reversingmembers disposed on opposite sides of the desired neutral position ofsaid movable member, means intermittently to effect engagement of saidmovable member with an impedance of said network to provide for responseof said responsive means to unbalance of said network and, whendisplaced from neutral position, selectively to efiect actuation of oneof said reversing members, means controlled by said responsive means toeffect rapid rebalancing adjustment of said network, and meanscontrolled by said reversing members to eflect slower, unbalancingadjustment of said network.

4. A system for regulating the magnitude of a condition comprising aplurality of independently balanceable networks having an impedance incommon, a plurality of electro-responsive means individual to saidnetworks, a plurality of regulating members individually adjustable toaflect the magnitude of said condition, a movable contact memberpositioned in accordance with the magnitude of said condition, reversingmembers disposed on opposite sides of the desired neutral position ofsaid contact member, means intermittently to effect engagement of saidcontact with said common impedance to provide for response of each ofsaid responsive means to unbalance'of its associated network, aplurality of means each controlled by one of said responsive means toeflect rebalanclng adjustment of the network associated therewith andconcurrent adjustment of one of said regulating members, and meanscontrolled by said reversing members to effect slower, unbalancingadjustment of all of said networks.

5. Control apparatus comprising an" electrical contact member deflectingin response to change in magnitude of a condition, a slide-wire movableto engage said contact member, spaced switchoperating members, and meansfor moving said slidewire intermittently to engage said contact memberand to effect engagement of said contact member with one of saidswitch-operating members in dependence upon sense-of its deflection fromposition corresponding with a predetermined magnitude of said condition.

'6. Control apparatus comprising an electrical contact member deflectingfrom a neutral position in response to change in magnitude of acondition, a slidewire movable to engage said contact member, spacedswitch-operating members, and means including cam structure for movingsaid slidewire intermittently to eilect engagement of said contactmember therewith and also to eflect intermittent engagement of saidcontact member with one or the other or said switch-operating members independence upon the sense of its deflection from neutral and for timessubstantially proportional to the magnitude of the deflection.

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